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Moving Charges And Magnetism
Question
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Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the centre of the ring is 

  • μoqf  / 2R

  • μoq / 2fR

  • μoq / 2πfR

  • μoqf / 2πR

Answer

A.

μoqf  / 2R

B = μoi / 2R
q = it 
 ⇒ i = q /t = qf
B = μoqf  / 2R

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Some More Questions From Moving Charges And Magnetism Chapter

Two moving coil meters, M1 and M2 have the following particulars:
R1 = 10 Ω   N1 = 30,
A1 = 3.6 x 10–3 m2,  B1 = 0.25 T
R2 = 14 Ω;  N2 = 42,
A2 = 1.8 x 10–3 m2, B2 = 0.50 T
(The spring constants k are identical for the two meters).
Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of M2 and M1.